Resistance metal heater



Dec. 24, 1968 A. T. RIZZOLO ETAL 3,418,447

RESISTANCE METAL HEATER Filed Sept. 1, 1965 4 Sheets-Sheet. l

. l NVENTORS:

ALFRED T.RIZZOLO WARREN F. HICKS THEIR ATTORNEYS Dec. 24, 1968 A. T. RIZZOLO ET AL I 3,418,447

RESISTANCE METAL HEATER Filed Sept. 1, 1965 4 Sheets-Sheet 2 INVENTORS ALFRED TRIZZOLO WARREN F. HICKS THEIR ATTORNEYS Dec. 24, 1968 RIZZQLQ ET AL 3,418,447

" RESISTANCE METAL HEATER Filed Sept. 1, 1965 4 Sheets-Sheet 5 TH EIR ATTORN EYS A. T. RIZZOLO ET AL 3,418,447 RESISTANCE METAL HEATER Dec. 24, 1968 4 Sheets-Sheet 4 Filed Sept. 1, 1965 United States Patent Ofice 3,418,447 RESISTANCE METAL HEATER Alfred T. Rizzolo, Newark, and Warren F. Hicks, Wayne, N.J., assignors to Cheston Company, Kearny, 'N.J., a corporation of New Jersey Filed Sept. 1, 1965, Ser. No. 484,194 9 Claims. (Cl. 219-156) ABSTRACT OF THE DISCLOSURE An electrical resistance heater has a channel shaped storage member into which like pieces of rod stock are loaded and from which they are fed sequentially by gravity and moved to a clamping position between spaced pairs of electrodes. The electrodes in each pairare inovable towards one another to grip the opposite ends of a piece to be heated, and away from one another to release the heated piece. The pairs of electrodes are yieldingly mounted for movement away from one another so as to enable them to accommodate any longitudinal expansion of the clamped stock piece during the heating operation.

This invention relates to improvements in resistance heaters for heating stockpieces such as, for example, bars, rods and the like prior to hot forging or other hot metal working operations and it relates particularly to feeding mechanisms for automatic resistance heaters and improvements in the electrode mounts therefore to prevent deformation of the stock pieces during heating.

Resistance type heaters are well known and many different types of control circuits, electrode mounts and feeding devices for such heaters have been provided heretofore. In general, the prior resistance heaters include sets of electrodes for engaging spaced apart portions of the article to be heated. The heating current is supplied and controlled by means of a saturable core reactor and a transformer having primary and secondary windings for applying a low voltage, high amperage current to the stock pieces gripped by the electrodes. The temperatures to which the stock pieces are heated may be controlled in various ways, for example, by means of thermostats, photoelectric eye circuits and the like which regulate the current supplied to the transformer.

In the heating of stock pieces, thermal expansion usually occurs and in order to avoid buckling or deformation of the stock pieces, provisions have been made for compensating for the thermal expansion, usually by gripping the stock piece, subjecting it to tension and forcing it against the electrodes by means of which the heating current is. supplied to the stock piece.

In accordance with the present invention, stock feeding systems are provided whereby stock pieces can be supplied to and supported for engagement by the electrodes so that stock pieces can be heated successively and in timed relation to supply a succession of undeformed heated stock pieces to forging equipment and the like.

More particularly, in accordance with the present invention, resistance heaters are provided with a pair of relatively fixed spaced apart electrodes for engaging stock pieces adjacent to their ends and a pair of movable electrodes which are adapted to move into engagement with a stock piece to grip it securely and allow high amperage current to flow through the stock piece to heat it to a desired temperature, the heater being provided with feeding means which feeds stock pieces successively 3,418,447 Patented Dec. 24, 1968 into contact with the fixed electrodes and retains them in proper position for engagement by both the fixed and movable electrodes prior to and during heating. In the new resistance heater, one pair or both pairs of fixed and movable electrodes are suitably mounted so that they can move against spring pressure in a direction to permit expansion of the stock piece while it is undergoing heating to avoid buckling or otherwise deforming the stock pieces.

The operation of the feeding means and the movements of the electrodes are affected in timed relation to enable the automatic feeding, heating and discharge of the stock piece without the need for temperatureresponsive means to regulate the temperature to which the stock piece is heated during the heating operation. The new feeding apparatus is adjustable to accommodate stock pieces of different sizes and to enable a series of heating units to be arranged so that the feeding means of all of the units can be adjusted simultaneously to accommodate stock pieces of varying length.

For a better understanding of the present invention, reference may be had to the accompanying drawings, in which:

FIGURE 1 is a view in side elevation and partially broken away of a resistance heater embodying the present invention;

FIGURE 2 is a front elevational view thereof;

FIGURE 3 is a plan view thereof partially shown in section and partially broken away illustrating the operation of the stock feeding mechanism;

FIGURE 4 is a plan view thereof showing the stock feeding mechanism in another position;

FIGURE 5 is a side elevational and partial sectional view of a mount for supporting a movable electrode and the motor for advancing and retracting the electrode;

FIGURE 6 is a view in section taken on line 6--6 of FIGURE 5;

FIGURE 7 is a side elevational view of a mount for the fixed electrode;

FIGURE 8 is a view in section taken on line 8-8 of FIGURE 7;

FIGURE 9 is a fragmentary and partial sectional view of the stock feeding apparatus of the resistance heater embodying the present invention; and

FIGURE 10' is a schematic wiring diagram of a control circuit for the resistance heater.

The form of resistance heater embodying the present invention chosen for purposes of illustration includes a supporting frame 10 provided with an upper fixed platelike platform or support 11 adjacent the mid portion thereof and another supporting plate portion 12 adjacent the left hand end thereof as viewed in FIGURE 1. Extending upwardly from the platform 11 are a pair of plate-like side frame members 13 and 14 in which are rotatably received a pair of threaded screw shafts 15 and 16. A pair of sleeves 17 and 18 on an angle-like support 19 receives the shafts 15 and 16 slidably to enable the adjustment of the plates along the shafts. Pairs of nuts 20, 21, 22 and 23 are threaded on the shaft and engage the opposite ends of the sleeves 17 and 18 to permit adjustment of the support 19 toward and away from the plates 13 and 14. Mounted on the angle member 19 is a guide member 24 which at its upper end is inclined downwardly and has a supporting plate 25 and a flange member 26 for guiding one end of a series of stock pieces S. I

A similar guide member 27 is also supported on the shafts and 16 and is similarly constructed for engaging the opposite ends of the stock pieces. The angle member 19 associated with each of the guides 24 and 27 closes the back side of the guide and thereby provides a channel shaped portion through which the stock pieces S are fed downwardly by gravity in a generally vertical direction toward the supporting plate 11.

Slidably mounted on the supporting plate member is an ejecting plate 28 which as shown in FIGURES 3 and 4 has forwardly projecting arms 29 and 30 thereon with inwardly projecting portions 31 and 32 providing notches 33 and 34 for receiving the ends of the lowermost stock piece S in the guides 24 and 27.

It will be apparent that by adjusting the nuts 20 to 23 along the shafts 15 and 16 the spacing between the guides 24 and 27 can be adjusted to receive stock piece S of different lengths. A plurality of such units may be mounted in side-by-side relation. To accommodate stock pieces of varying length, the front sections of the ejecting plate 28 can be replaced or made adjustable in width, if so desired. The ejecting plate 28 is reciprocated on the supporting plate 11 by means of a suitable air cylinder or air motor 35 which is fastened to a plate or other support 36 connected to or forming a part of the support 11. A connecting rod 37 of the air motor is connected by means of a clevis 38 to an upstanding lug 39 on the ejecting plate 28 so that upon projection of the connecting rod, the slide plate is moved to the left and upon retraction of the connecting rod the ejecting plate is moved to the right as viewed in FIGURE 1.

As shown in FIGURES 1, 3 and 4, the notches 33 and 34 are disposed in alignment with the lower end of the guides 24 and 27 so that a stock piece S can drop into the notches 33 and 34. As the slide plate 28 is moved to the left (FIGURE 1) by means of an air cylinder or motor 35, the stock piece engaged in the notches is also moved to the left until it drops over the left-hand edge of the supporting plate 11. The stock piece above the one being ejected engages the upper surface of the ejecting plate 28 and cannot drop down to interfere with the movement of the. slide plate. As the stock piece moves beyond the edge of the plate 11, it drops down onto a guide (FIG- URES 1, 2 and 9) which includes a pair of guide fingers 40 and 41, one of which is shown in FIGURE 9. The guide finger 41, for example, is a lever which is pivotally supported in a clevis 42 mounted on a-shaft-43 which is fixed to and movable with the ejecting plate 28 by means of a pair of nuts 44 and 45, The shaft 43 and the nut 44 areslidable in a slot 46 in the support plate 11 so that the lever 41 moves with the slide plate 28 between the full line position and the dotted line position shown in FIGURE 9. At the right-hand end of the lever 41 is a counterweight 47 which normally holds the guide finger in a horizontal position.

Referring now to FIGURES 2 and 9 the guide fingers 40 and 41 carry an inverted channel shaped guide plate 47 on their upper surfaces, the plate being fixed to the left-hand end of the levers as viewed in FIGURE 9 and spanning the space between them and serving to receive and support a stock piece. The weight of the stock piece tilts the plate and fingers downwardly so that the stock piece will roll into engagement with the fixed electrodes 50 and 51 of the heater as best shown in FIGURES 4 and 9.

Another pair of cooperating electrodes 52 and 53 is mounted for sliding movement toward and away from the electrodes 50 and 51 to grip the ends of a stock piece between them and support it for passage of current therethrough to heat it. Each of the electrodes 52 and 53 is moved toward and away from the electrodes 50 and 51 by means of an air cylinder or motor 54. As will be explained hereinafter, one pair of electrodes 50 and 52 or 51 and 53 or both pairs of electrodes are mounted for movement generally axially of the stock piece to allow endwise expansion of the stock piece as it is heated.

Referring now to FIGURES l, 7 and 8, each of the electrodes and 51 is mounted in similar electrode clamps which may suitably consist of a rectangular block having a forwardly extending flange 56 and a removable clamp member 57 secured by means of a stud and nut 58 for engaging the electrode 50 and securing it in position. The clamp 55 is mounted on an angle member 59 by means of one or more studs and nuts 60 or screws. The angle member 59 has a horizontally extending arm 61 provided with a pair of sleeves 62 and 63 welded or otherwise secured thereto. Teflon or other bushings 64 are mounted in each of the sleeves 62 and 63 to make them readily slidable on the shafts 65 and 66 which are fixed in a downwardly opening channel member 67 fixed to and beneath the platform 12.

As shown in FIGURES l and 8, the sleeves 62 and 63 are of lesser length than the spacing between the flanges 68 and 69 on the channel member so that limited sliding movement of the sleeves and the electrode 50 supported thereby is possible.

As shown in FIGURE 8, a coil spring 70 is interposed between the outer ends of the sleeves and the flange 69 of the channel so that the sleeves and the electrode 50 can move in the direction of expansion of the stock pieces during heating to allow the stock piece to expand. As indicated above, one or both of the electrodes 50 and 51 are similarly mounted and are movable against spring pressure in a direction to permit thermal expansion of the stock piece.

A similar mounting means is provided for one or both of the movable electrodes 52 and 53. As shown in FIGURES 5 and 6, an air motor or cylinder 54is mounted on a plate 72 which is welded at its inner end to a tubular sleeve 73. The sleeve 73 extends crosswise of a tubular guide member 74 which also carries another transversely extending tubular sleeve 75 thereon. The sleeves 73 and 75 are provided with Teflon bushings 76 for sliding movement on the shafts 77 and 78 which are fixed in the inverted channel member 79 fixed to a supporting plate 80 mounted in the frame 10'. Springs 81 are interposed between the ends of the sleeves 73 and 75 and the flange 82 of the channel 79 to allow the air motor and the guide sleeve 74 to move against the pressure of the spring in the direction of thermal expansion of a stock piece while it is being heated. The guide 74 receives the air cylinder piston rod 83 and a coupling, not shown, for connecting the piston rod 83 to a guide shaft 84 on which the movable electrode 52 is mounted. The other electrode 53 is similarly mounted. If necessary, an insulated support 85 may be provided for aiding in guiding and supporting the movable electrodes 52 and 53.

It will be apparent, therefore, that the electrodes 52 and 53 can be moved toward the fixed electrodes 50 and 51 to grip a stock piece between them and away from the fixed electrodes to discharge a stock piece and receive another stock piece for heating therebetween.

In operation, the movements of the components described above take place in timed relation. With the electrodes 52 and 53 and the ejecting plate 28 retracted, the notches 33 and 34 are in alignment with the stock feed guides 24 and 27 and receive a stock piece S therefrom. The first move-ment is the advancing of the ejecting plate 28 by means of the air motor 35 together with guide plate 47 and fingers 40 and 41 toward the dotted line portion shown in FIGURES 1 and 9 and the full line position shown in FIGURE 4 until the stock piece moved by the ejecting plate passes beyond the support platform 11 and drops onto the feed plate 47 causing it to tilt and allow the stock piece to roll down into engagement with the fixed electrodes 50 and 51. The movable electrodes 52 and 53 are then advanced by means of the air motors 54 to grip the ends of the stock piece between them and the electrodes 50 and 51. As soon as the stock piece is gripped by the electrodes, the ejecting plate 28 and the guide plate 47 and fingers 40 and 41 are retracted by means of the air motor 35 and thereafter current is passed between the electrodes at opposite ends of the stock pieces to heat it by its resistance. When the stock piece has been heated for a predetermined period of time, the movable electrodes 52 and 53 are retracted by means of their air motors allowing the heated stock pieces to drop down into a chute 86 or onto a conveyor to be'carried away to a hot forging press or the like. The above-described operation is repeated to supply a succession of heated stock pieces.

The cycle of operations described above can be accomplished with the circuit disclosed in FIGURE 10.

The resistance heater circuit illustrated schematically in FIGURE includes a saturable core reactor 90 connected with the primary winding 91 of a transformer, the secondary winding of which is represented by the electrodes 50, 52 and 51, 53. A control coil 92 for the reactor is connected to a rectifier 93 having one terminal connected by means of conductor 94 to one terminal 95 of a source of electrical energy such as 110 volt, 6O cycle alternating current. The other terminal 96 of the rectifier 93 is connected to a powerstat 97 which is connected with the other terminal of the source of electrical energy in a manner to be described hereinafter.

The main power supply, for example, 440 volt, 60 cycle alternating current, for the reactor 90 and the transformer is connected to the terminals 98 and 99. Interposed between the terminal 98 and one winding of the reactor 90 is a multiple contact relay switch 100 having a relay coil 101 by means of which the electrodes are energized and de-energized.

The control circuit for the resistance heater unit includes a selector switch 102 for manual or automatic control of the operation of the components of the unit. The movable contact of the selector switch 102 is connected by means of conductor 103 to the power source terminal 104. This movable contact 105 can be moved between off dead contact 106, a manual operation contact 107 and an automatic operation contact 108.

A program timer 109 is connected by means of a conductor 110 to the automatic operation contact 108 and includes an electrically actuated timer and a switch 111 which is opened and closed by means of the timer to initiate a series of complete operational cycles of the heater. For example, the program timer 109 may be set to start a complete feeding and heating cycle and after a period of time such as for example, a half minute or some other suitable time to start another cycle and repeat such cycles as often as desired. As shown, the movable contact 112 of the switch 111 is connected to the conductor 110 and the other contact is connected by means of a conductor 113 to the movable contact 114 of a switch in a relay 115. The fixed contact 116 of the switch is connected by means of a conductor 117 to the conductor 110 forming a holding circuit around the switch 111. Also, the conductor 113 is connected by means of a conductor 114 to a conductor 119 which is connected to one terminal of the relay coil 120 of the relay 115, the other terminal of the coil 20 being connected by means of a conductor 121, a normally closed stop switch 122, a conductor 123 through the normally closed contacts 124 of a timer switch 125 and a conductor 126 to the conductor 94 and the terminal 95.

The manual contact 107 of the selector switch 102 is connected by means of a conductor 127 to a manually operated, normally open switch 128 and to the conductor 119. When the switch 128 is closed, a holding circuit can be closed around the starting switch 128 by means of a conductor 129 connected to the conductor 127 and to the movable contact 130 of a normally open switch in the relay 115, the fixed contact 131 being connected by conductor 123 to the conductor 119. In this way, when the movable contact 105 of the selector switch 102 is moved into engagement with manual contact 107 and the starting switch 128 is closed, the relay coil 120 will be energized by a circuit from the terminal 104 through conductor 103, contact 105, contact 107, conductor 127, closed starting switch 128, conductor 119, solenoid 120, conductors 121, switch 122, conductor 123, closed relay switch 124, conductor 126, conductor 94 to terminal 95. Energizing the relay coil closes all of the contacts of relay 115. Inasmuch as a relay contact engages contact 131, a holding circuit is created through the contacts 130 ,131, contact 132 and solenoid coil 120 so that the coil 120 remains energized even though the starting switch 128 is opened.

In the same way, relay coil 120 can be energized,

by moving the selector contact 105 into contact with contact 108. The program timer switch 111 will close momentarily in response to operation of the timer so that a circuit is completed from terminal 104 through conductor 103, contacts 105 and 108, conductor 110, closed switch 111, conductors 113, 118, 119 to the coil and thence to terminal 95. Inasmuch as all contacts of the relay 115 are closed, a holding circuit around switch 111 is closed through conductor 117, relay contacts 114 and 115 and conductors 118 and 119 to the relay coil 120.

Closing of the contacts of the relay 115 also completes other circuits as follows: Connected to the conductor 103 is a limit switch 133 having a movable contact 134 and fixed contacts 135 and 136. The movable contact 134 is connected to conductor 103 by a conductor 137. With the contacts 134 and 135 in engagement as shown, a circuit is completed from terminal 104 through conductors 103 and 137, contacts 134 and 135, through a solenoid coil 138 of a solenoid actuated valve 139 which controls the supply of air to and discharge of air from the air motor 35 to advance the ejecting plate 128 to feed a stock piece between the electrodes. When the ejecting plate has moved forward far enough to discharge a stock piece into engagement with the electrodes 50 and 51, the movable contact 134 is shifted by the ejector plate into engagement with the contact 136. When the movable contact 134 disengages the contact 135, the solenoid 138 is de-energized and air is vented from the air motor or supplied to the opposite end thereof to cause the ejecting plate to be retracted. When the limit switch contacts 134 and 136 engage another circuit is completed from terminal 104, conductor 103, conductor 137, contacts 134, 136, conductor 140, closed contacts 141 and 142 of relay 115, conductor 143, relay coil 144, conductor 145, and conductor 94 to terminal 95. When the relay coil 144 is energized, its normally open contacts 146 and 147 close, thereby energizing the coil 148 of a relay 149 as follows: terminal 104, conductor 103, conductor 150, relay contacts 146, 147, conductor 151, relay coil 148, conductor 152, conductor 94 to terminal 95.

Energization of relay 115 also energizes the air motor 54 for advancing the movable electrodes 52 and 53 in the following manner: from terminal 104 through conductor 103, conductor 154, closed relay contacts and 156, conductor 157, relay coil 158 and conductor 159 to conductor 94 and terminal 95 thereby energizing relay coil 158 which closes its normally open contacts 160 and 161. Closing of these contacts energizes the solenoid valve 162 to supply air to the air motors 54 to advance the movable electrodes 52 and 53 by means of a circuit from terminal 104, conductor 103, conductor 163, contacts 160, 161, solenoid valve 162, conductor 164, conductor 94 to terminal 95 whereby the electrodes are advanced to grip the workpiece. This circuit is closed before the ejecting plate engages the limit switch 133.

In order to energize the reactor 90 the transformer winding 91 and the electrodes 52 and 53, the switch 100 must be closed by means of its relay coil 101. This occurs upon energization of the relay coil 148 as described above by means of the following circuit: terminal 104, conductor 103, conductor 165, closed relay contacts 166, 167, relay coil 101, conductor 1'68, contactor 169, conductor and terminal 95. Energizing of the relay 7 101 closes all of the contacts of the switch 100 and thereby starts the heating operation.

Near the end of the heating operation, it may be found desirable to reduce the current flow through the workpiece to avoid overheating of the workpiece and to that end, a circuit is provided which introduces an increased resistance into the input of the rectifier 93.

A resistance timer 171 is provided in order to shunt out a rheostat 172 which is connected in series with the powerstat 97. Thus, a circuit is closed from the terminal 104, through conductor 173, closed relay contacts 174, 175, conductor 176 to the relay coil 178 of the resistance timer. The resistance timer determines the time at which the normally closed relay contacts 179 and 180 are opened. The resistance timer is started by the program timer and may be a part thereof, if desired. The resistance timer 178 is also connected by means of a conductor 181 to conductor 94 and terminal 95 thereby completing the circuit to open the contacts 179.

Closing of the contacts 182 and 183 of the relay 149 supplies energizing current to the rectifier 93 and control coil 92 as follows: terminal 104, conductor 103, conductor 184, closed contacts 182 and 183, conductor 185, closed contacts 179 and 180, conductor 186 and conductor 187 to one terminal of the powerstat 97, its other terminal being connected by means of conductor 188 to conductor 94 and terminal 95. Also the rheostat 172 is connected by means of a conductor 189 to the conductor 185 and its adjustable contact 190 is connected to the conductor 187 so that it is shunted out of the powerstat rectifier circuit when the contacts 179 and 180 are engaged. However, as indicated above, after a predetermined interval, the resistance timer causes the contacts 179 and 180 to open whereupon current flows through the rheostat 172 and powerstat 97 increasing the resistance and decreasing the current flow to the rectifier and thereby reducing the heating rate of the stock piece.

Timing of the complete heating cycle is controlled by means of the heat timer 125 under the control of the contacts 193 and 194 of the relay 149. The heat timer includes a normally closed switch 124 which is opened momentarily by the heat timer 192 to terminate a heating cycle. Thus, when the relay coil 148 is energized, current flows from the terminal 104 into conductor 103, conductor 196, relay contacts 193 and 194, closed switch 195, the timing element 197 of heat timer 125, conductor 198 and conductor 94 to terminal 95. The timing element 197 terminates an operating cycle by opening switch 124 momentarily. When relay switch 124 opens, the circuit through relay coil 120 of-relay 115 is opened and all of its contacts move to the open position which in turn de-energizes relay coils 148, switch coil 101, relay coil 158 and relay 144 thereby restoring the circuit to its initial condition and opening the switch 100 which shuts off the supply of power to the electrodes of the resistance heater.

When, in automatic operation, the program timer again closes its switch 111, the cycle is repeated in the manner described generally above to feed a stock piece between the electrode jaws by advance of the ejector plate 28, the electrodes 52 and 53 are advanced to grip the stock piece, the ejector plate 28 is retracted by actuation of the limit switch 133, the electrodes are energized with a low resistance in the rectifier circuit and then the resistance is increased by connecting in the rheostat 172 and thereafter the heat timer 125 discontinues heating and restores all of the elements to their initial position. Retraction of the ejecting plate 28 restores the limit switch 133 to a condition in which the switch contacts 134 and 135 are in engagement ready for another cycle of operation.

The above-described circuit does not require any heat responsive-means for control of the temperature of the workpiece being heated. However, thermostatic, pyrometic photoelectric or other temperature sensing or responsive means may be included to control the heating of the workpiece.

Other variations and modifications of the circuit and the apparatus are possible without departing from the invention and accordingly, the form of the invention disclosed herein should be considered as illustrative.

We claim:

1. An electric resistance heater for heating workpieces comprising a first pair of electrodes, a second pair of electrodes, means for moving one pair of opposed electrodes toward the other pair of electrodes to grip opposite end portions of a workpiece and away from said other pair of electrodes to release said workpiece and receive another workpiece, means for supplying electrical current to said electrodes to heat a workpiece gripped by said pairs of electrodes, platform means above said pairs of electrodes having an edge spaced from and above said electrodes, guide means extending upwardly from said platform for receiving a plurality of workpieces for downward movement toward said platform means, an ejecting member between said platform means and said guide means, an opening in said ejecting member for receiving the lowermost of said workpieces, means for moving said ejecting member parallel with said platform means to a position in which said opening is disposed beyond said edge to discharge the workpiece in said opening downwardly and means movable with said ejecting member for guiding said discharged workpiece into engagement with one pair of said electrodes.

2. The resistance heater set forth in claim 1 in which said means movable with said ejecting member comprises a guide plate pivotally connected to said ejecting member below said platform means, means urging said guide plate to a substantially horizontal position, said guide plate being movable to an inclined position by the weight of a workpiece to guide said workpiece into engagement with said one pair of electrodes.

3. The resistance heater set forth in claim 1 in which said means movable with said ejecting member comprises supporting members extending downwardly from said ejecting plate, means in said platform means receiving said supporting members for movement toward and away from said edge, a guide lever pivotally connected to each of said supporting members below said platform member, a guide plate extending between and connecting said guide levers, and means for biasing said levers and guide plate into a substantially horizontal position.

4. The resistance heater set forth in claim 1 comprising means supporting one electrode of one pair of elec trodes and an Opposing electrode of the other pair of electrodes for movement toward and away from the other electrodes of said pairs, and means biasing said one opposed electrodes toward said other electrodes to enable the thermal expansion of a workpiece gripped by said pairs of electrodes.

5. In the resistance heater set forth in claim 1, mounts for an electrode of each pair of electrodes comprising a first, fixed channel member, a pair of spaced-apart rod members spanning said channel member and extending substantially parallel with said edge, sleeves mounted on said rod members for sliding movement lengthwise of said rod members, an electrode support connected to and supported by said sleeves with said electrode substantially perpendicular to said guide rods, and spring means at one end of said sleeves biasing said sleeves and said electrode support toward the other electrode of the corresponding pair.

6. In the resistance heater set forth in claim 5, a motor mounted on one of said electrode supports for moving one of said electrodes toward and away from an opposing electrode.

7. An electrode mount for an electric resistance heater comprising a channel member having spaced apart flanges, a pair of substantially parallel rod members extending between said flanges, a sleeve slidable lengthwise of each rod member between said flanges, an electrode support fixed to said sleeves and including electrode car rier means movable in a direction substantially perpendicular to said sleeves to engage a piece to be heated, and spring means between one of said flanges and an end of each sleeve biasing said sleeves and support toward the other flange.

8. The electrode mount set forth in claim 7 in which said support comprises a clamp for gripping an electrode.

9. The electrode mount set forth in claim 7 in which said support comprises a tubular guide haying an axis substantially perpendicular to the axes of said sleeves, a shaft slidably mounted in said tubular guide, a motor supported by saidg sleeve for reciprocating saidshaft axial- 15 ly and means connecting said shaft to an electrode.

10 References Cited UNITED STATES PATENTS 402,416 4/1889 Dewey 219-162 1,599,097 9/1924 Bisset et a1. 219-156 1,697,811 1/1929 Dailey 219-156 X 1,968,443 7/1934 Clark et a1 219156 X 2,003,486 6/1935 Hankins 219-156 X RICHARD M: WOOD, Primary Examiner. B. A. STEIN, Assistant Examiner.

US. Cl. X.R. 21950, 119, 156 

